A compact and thin-type image pickup apparatus has come to be mounted on a mobile terminal representing a compact and thin-type electronic hardware (such as a cell phone and PDA (Personal Digital Assistant)), whereby, it has become possible to transmit mutually not only voice information but also image information to a remote location. As image pickup elements used for these image pickup apparatuses, a solid-state imaging device such as an image sensor of a CCD type and an image sensor of a CMOS type are used.
In recent years, an image pickup element with fine pixel pitch has been employed for an image pickup apparatus with a wide angle of view to be mounted on a mobile terminal, for the purpose of downsizing of the image pickup apparatus. Such the trend continues to be furthermore accelerated. However, an image pickup element with a small pixel pitch exhibits a deteriorated SN ratio under a lower brightness condition, which becomes a cause of noise. To solve it, a development of an image pickup lens having a small F-number, and a high performance of representation has been required. At the same time, telecentricity has also been required for solving an insufficient light-amount of a ray to be formed into an image on a periphery of the image area. To respond to such the requirements, Patent Literatures 1 and 2 propose image pickup lenses in which the F-number is set to be as small as 2.4 to 2.8. Further, Patent Literatures 3 to 7 propose image pickup lenses aimed at a realization of mass production.